Miocene detachment faulting predating EPR propagation: Southern Baja California

Type Article
Date 2016-05
Language English
Author(s) Bot Anna1, Geoffroy Laurent1, Authemayou Christine1, Bellon Herve1, Graindorge David1, Pik Raphael2
Affiliation(s) 1 : Univ Bretagne Occidentale, UMR 6538, LDO, IUEM, Plouzane, France.
2 : Univ Lorraine, CNRS, UMR 7358, CRPG, Nancy, France.
Source Tectonics (Amer Geophysical Union), 2016-05 , Vol. 35 , N. 5 , P. 1153-1176
DOI 10.1002/2015TC004030
WOS© Times Cited 9
Abstract

At the southern tip of the Baja California peninsula, we characterize the onshore structures and kinematics associated with crustal necking leading up to the Pliocene breakup and early East Pacific Rise seafloor spreading. From a combination of tectonic field investigations, K-Ar and cosmogenic isotope dating and geomorphology, we propose that the Los Cabos block represents the exhumed footwall of a major detachment fault. This north trending detachment fault is marked by a conspicuous low-dipping brittle-ductile shear zone showing a finite displacement with top to the SE ending to the ESE. This major feature is associated with fluid circulations which led to rejuvenation of the deformed Cretaceous magmatic rocks at a maximum of 17.5Ma. The detachment footwall displays kilometer-scale corrugations controlling the present-day drainage pattern. This major detachment is synchronous with the development of the San Jose del Cabo Basin where syntectonic sedimentation took place from the middle Miocene to probably the early Pliocene. We propose that this seaward dipping detachment fault accommodates the proximal crustal necking of the Baja California passive margin, which predates the onset of formation of the East Pacific Rise spreading axis in the Cabo-Puerto Vallarta segment. Our data illustrate an apparent anticlockwise rotation of the stretching direction in Baja California Sur from similar to 17 Ma to the Pliocene.

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